The Robert Bosch VE distributor/rotary injection pump is available with one of two mechanical governors to control the speed and response of the engine. These two types of governors and their functions are:

1. Variable-speed governor: controls all engine speed ranges from idle up to maximum rated rpm. With this governor, when the throttle lever is placed at any position, the governor will maintain this speed within the droop characteristics of the governor. The variable-speed governor and its operation are illustrated in Figures 19-77a and 19-77b with its actual location in relation to the other injection pump components being clearly shown in Figure 19-68.

2. Limiting-speed governor: sometimes known as an idle and maximum speed governor since it is designed to control only the low- and high-idle speeds (maximum rpm) of the engine. When the throttle lever is placed into any position between idle and maximum, there is no governor control.Any change to the engine speed must be determined by the driver/operator moving the throttle pedal. This governor is shown in Figure 19-77c.

The variable-speed governor can be used on any application where all-range speed control is desired such as on a stationary engine or on a vehicle that drives an auxiliary power takeoff (PTO).

All model VE pumps use a percentage of the fuel delivered to the injection pump housing to cool and lubricate the internal pump components. Since the diesel fuel will pick up some heat through this action, a bleed off or fuel return from the injection pump housing is achieved through the use of a hollow bolt with an orifice drilled into it as shown in Figure 19-74.

This bolt is readily identifiable by the word OUT stamped on the hex head, and if substituted with an ordinary bolt, no fuel will be able to return to the fuel tank from the injection pump.

Contained within the hydraulic head (outlets) of the injection pump where the high-pressure fuel lines are connected to the injection pump are delivery valves (one per cylinder) (Figure 19-73), which are designed to
open at a fixed pressure and deliver fuel to the injectors in firing-order sequence.

These valves function to ensure that there will always be a predetermined fuel pressure in the fuel lines leading to the fuel injectors. Another major function of these individual delivery valves is to ensure that at the end of the injection period for that cylinder there is no possibility of secondary injection and also that any pressure waves during the injection period will not be transferred back into the injection pump.

If secondary injection were to occur, the engine would tend to misfire and run rough. The delivery valves ensure a crisp cutoff to the end of injection when the fuel pressure drops off in the line and also maintains fuel in the injection line so that there is no possibility of air being trapped inside the line.

Within the various chapters of this book are featured a number of high-technology diesel fuel injection control systems, with DDC’s DDEC system (late 1985), Caterpillar’s PEECsystem (early 1987),and Cummins ECI system (1989)being mass-produced designs that have gained prominence since late 1985.The Robert Bosch Corporation offers electronic sensing and control of both its heavy-duty inline multiple-plunger pumps and its smaller model VE distributor pump assemblies used in automotive applications. As with the DDC and Cat systems, the high pressures necessary for injection purposes are still created mechanically by a reciprocating plunger within a barrel; however, control of the fuel rack position, and therefore of the quantity of fuel injected for a given throttle position and load, is determined by an ECU(electronic control unit) which has been programmed to output specific control signals to the governor / rack in relation to the accelerator position, turbocharger boost pressure, mass airflow rate, engine oil pressure, and temperature and coolant level.

In naturally aspirated (non turbo charged) diesel engines such as cars or trucks that can travel through varying terrain and altitudes, a means by which the fuel delivery rate can be altered is an important function of the governor and altitude pressure compensator. Since atmospheric pressure decreases with an increase in altitude, the volumetric efficiency of the engine will be less at higher elevations than it will be at sea level. On turbocharged engines, a boost compensator performs a function similar to that of the altitude compensator on nonturbocharged engines. Bosch refers to the altitude compensator as an ADA mechanism, and it is used in conjunction with either the RQ or RQV mechanical governor models. The ADA is located on the governor cover.

Basically, the boost compensator ensures that the amount of injected fuel is in direct proportion to the quantity of air within the engine cylinder to sustain correct combustion of the fuel and therefore increase the horsepower of the engine. With the engine running, pressurized air from the cold end of the turbocharger passes through the (Figure 19-63b) connecting tube from the engine air inlet manifold to the boost compensator chamber. Inside this chamber is a diaphragm (Figure 19-63a) which is connected to a pushrod, which is in turn coupled to the compensator lever. Movement of the diaphragm is opposed by a spring, therefore for any movement to take place at the linkage,
the air pressure on the diaphragm must be higher than spring tension. As the engine rpm and load increase and the air pressure within the connecting tube becomes high enough to overcome the tension of the diaphragm spring, the diaphragm and pushrod will be pushed down.

This movement causes the compensator lever to pivot, forcing the fuel control rack toward an increased fuel position. The boost compensator will therefore react to engine inlet manifold air pressure regardless of the action of the governor. When the turbocharger boost air pressure reaches its maximum, the quantity of additional fuel injected will be equal to the stroke of the aneroid boost compensator linkage, in addition to the normal full-load injection amount that is determined by the governor full-load stop bolt.

The RQV governor is a variable-speed mechanical unit that employs the governor springs assembled into the weights in the same manner as that for other RQ models. As such, it controls idle speed, maximum speed, and any speed range in between at which the operator places the throttle linkage. Figure above illustrates the pear-shaped housing of the RQV governor, which is also found on all other RQ models.

The RQV governor is used with the models M,A,MW,and P Bosch inline multiple-plunger pumps, as well as on the VA and VE models of Bosch distributor pumps. Major truck engine manufacturers that use RQV variable-speed governor are Deutz, Fiat Allis, Navistar (International Harvester), Mack, Mercedes-Benz, and Volvo.The RQVis employed on vehides with auxiliary drive, such as garbage compactor trucks, tanker trucks, and cement mixer trucks, to control the PTO (power takeoff) applications. Since the RQV is a variable-speed (all-range) governor, it operates on the same basic principle as the RSV shown and discussed earlier in this chapter, the only difference being in the internal linkage arrangement. The RSVuses a starting and main governor spring, while the RQVhas the springs assembled inside the weight carrier.

The difference between the RQ governor model and the RQV is that since the RQV is an all-range variable-speed unit, and the RQ is a minimum/maximum (limiting-speed) unit, the weights in the RQV will move out throughout the complete speed range, and will not lose control between the end of the idle speed range and the start ofhigh-speed governing such as occurs within the RQ model.